>Well, you're the engineer, but if it takes 100lbs to compress the >soundboard 1", doesn't it take considerably more than that to compress it >the next inch? I don't know. Hence the reason for my initial post. My inclination is to say no. If you were to take a flat sheet or thin panel (or slightly curved or crowned sheet or panel - so slightly curved that curved beam effects are negligible), attach ribs to it, and support it at its ends (only vertical support - allowing the ends to move in and out) then I would expect the spring rate to be linear, as long as we were in the elastic range of the material. If it took 100 lbs to deflect this ribbed panel 1 inch, then it would take an additional 100 lbs to deflect it an additional 1 inch (actually, this is not realistic - those deflections are huge and you would start having non-linear effects - but assuming real world deflections for a real world panel I would expect the spring rate to be linear). Now attach this to a rigid rim or frame. If the geometry of the panel is not such that there can be any arch effects then I would expect the same result. If the geometry of the ribbed panel is such that there could be arch type loading, and if this arch loading did not cause the elastic limit of the material to be exceeded, then I would expect the spring rate to be non-linear, and I would expect the spring rate to be decreasing, not increasing, as the arch flattened out under increasing load. So, based on all this, I would not expect an increasing spring rate. If there is one, I'll have to see some data to be convinced. And then my question would remain, what's causing that to happen? > Doesn't that suggest a stiffening of the board as it's >compressed? > >David Love >davidlovepianos@earthlink.net If what you're positing actually occurred, then yes, it does suggest a stiffening of the board as it's compressed. Do you have any deflection vs. load data for a real board that demonstrates this? Phil Ford
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